Concrete is used for a variety of different purposes, such as road and building construction. It is especially common for buildings that are used for industrial purposes to have concrete flooring. Unfortunately, concrete made from conventional lime-containing cement is not well suited for use in structures that are exposed to high acidity, chemical leaching attack, or other harsh conditions. For example, in milk pasteurization plants, swimming pools, and other environments where acidic chemicals are present, the concrete made from conventional lime-containing cement degrades rapidly under conditions of normal use. Conventional concretes also suffer the problem of having long curing times. Conventional curing accelerators, such as calcium additives, often have the effect of reducing structural strength in the cured concrete. Various attempts have been made to provide concrete additives, such as polymers, that impart resistance to chemical attack and accelerate the time to cure.
Concretes incorporating polymeric additives, such as latex, vinyl esters, and polyester polymers, are known. For example, U.S. Pat. No. 5,576,378 describes a cement additive that may be mixed with lime mortar to comprise from 70 to 99 parts by weight of the cement-polymer mixture. The additive includes mono-unsaturated aromatic monomers, aliphatic conjugated diene monomers, esters of (meth)acrylic acid monomers, and monoethylenically unsaturated carboxylic acid monomers including the anhydride esters, amides, and imides thereof.
U.S. Pat. No. 4,777,208 describes the use of a polyester amide resin that may be mixed with an aggregate to form a polymer concrete which does not contain conventional lime mortar. The polyester amide variety of polymer concrete has not achieved widespread commercial use, in part, because of poor strength-to-cost performance. Additional strength may be obtained by adding additional resin, but the resin is the most expensive part of the admixture. The cost/performance analysis often results in another option meeting the performance design criteria more economically.
Polyurethanes are polyester amides, and conventional textbook reaction chemistry for producing polyurethanes involves reacting a polyol with an isocyanate, especially a dihydroxy alcohol with a diisocyanate. Polyurethane resin formulations have different contents corresponding to whether the polymerized composition is intended to be a fiber, a coating for concrete or the like, an elastomer, or a foam. For example, in foaming applications, a polyether, such as propylene glycol, may be treated with a diisocyanate in the presence of water and a catalyst, e.g., an amine or a tin compound. The water reacts with the isocyanate groups to provide crosslinking and also evolves carbon dioxide gas resulting in a foamed polymer.
Due to the cost/performance considerations mentioned above, polyurethanes are more commonly accepted for use as flooring sealants than as additives to concrete. A typical sealant may be formed, for example, by reacting a mixture of toluene and 4,4′-diphenyl-methane diisocyanates with a polyol. It is particularly problematic that, upon curing, these polymers generate potentially hazardous volatile organic compounds (VOCs) or vapor pollutants. Both the polyol and the diisocyanate contribute to the vapor pollution problem.
U.S. Pat. No. 6,107,433, which is hereby incorporated by reference to the same extent as though fully replicated herein, describes advancements in the art of polyurethane chemistry through the use vegetable oil-based polyols. The materials are less harmful to the environment than prior polyols in use, and they originate from renewable plant resources, such as soybean plants and the like. Vegetable oil-based polyols are formed by reacting a peroxyacid with vegetable oil to form an epoxy group. The epoxidized vegetable oil is added to a mixture of alcohol, water, and a catalytic amount of fluoboric acid to yield a vegetable oil-based polyol.
The polyol is optionally reacted with an isocyanate to yield a polyurethane. In forming the polyurethane, the isocyanate reacts with the hydroxyl groups of the vegetable oil-based polyol. The vegetable oil-based polyol and the isocyanate are combined in approximately stoichiometric quantities. It is acceptable to use up to about 10% in excess of the stoichiometric quantity of either of these components. A filler, such as silica, alumina, calcium carbonate, dolomite, silicates, glass, ceramics, clay, and talc may be added to the reaction mixture in amounts ranging from about 1% to 200% by weight of the vegetable oil-based polyol to form cast electroinsulators. Large amounts of filler are recommended, in order to enhance the electroinsulating properties of the cast resin. The vegetable oil-based polyurethanes have not heretofore been considered for use in polymer concretes.
It remains a problem in the art that there are no methods and materials available for forming polymer concretes, and particularly polyurethane concretes, from naturally occurring and renewable materials. It is a further problem that existing polyester amide concretes are not widely used due, at least in part, to poor cost performance.